1. Field of the Invention
The present invention relates to a power ratchet wrench and more particularly to an improvement in a power ratchet wrench for mounting and dismounting threaded items such as bolts, nuts and screws in, for instance, assembling, disassembling and maintaining automobiles and various other devices and structures.
2. Prior Art
Prior art power ratchet wrenches are disclosed in, for instance, Japanese Patent Application Laid-Open Nos. S63-28571, S63-256373, H6-35115 (S61-260982), H10-217140, and 2001-30179.
In these power ratchet wrenches, two sides of a yoke are received by opposing faces of a distal end bifurcated portion of a housing, and a spindle having a workpiece engagement portion, a small diameter portion, and a large diameter portion is inserted inside the yoke. The rotary motion of a motor provided on a proximal side of the housing is transmitted through a motion converter that converts a rotary motion into a reciprocal swing motion, thereby reciprocally rotating the yoke by way of using a center line of the spindle as a center of its rotational-motion, so that a ratchet pawl of a ratchet mechanism installed in a space inside the large diameter portion of the spindle is alternately engaged with and disengaged from an internal teeth formed around an inner peripheral surface of a hole of the yoke, thus causing the spindle to rotate in steps and causing a workpiece, such as a bolt, nut, screw, and the like, to turn with a workpiece engagement portion provided at one end of the spindle.
In above power ratchet wrenches, the internal teeth of the yoke are supported in the large diameter portion of the spindle. This structure will be described in detail with reference to FIG. 5.
Two sides of a yoke 1 are received by the opposing faces of the retaining elements 2bxe2x80x2 and 2bxe2x80x3 of the distal end bifurcated portion of a housing 2; and the yoke 1, using the center line of the spindle 3 inserted in the yoke 1 as its rotational center, reciprocally rotates by a motor 4 provided inside the proximal side of the housing 2 through a speed-reduction assembly 5, a power transmission shaft 6, and a motion converter 7 that converts a rotary motion into a reciprocal swing motion. As a result, the ratchet pawl 8a of a ratchet mechanism 8 installed inside the large diameter portion 3c of the spindle 3 is alternately engaged with and disengaged from an internal teeth 1a of the yoke 1, thus causing the spindle 3 to rotate in steps and to turn the workpiece, such as a bolt, nuts and screws, with the workpiece engagement portion 3a provided at the distal end of the spindle 3.
The power ratchet wrench disclosed in Japanese Patent Application Publication (Kokoku) H6-35115 has a hammer structure that provides hammer rotation in place of the speed-reduction assembly 5.
As generally known, the ratchet mechanism 8 comprises a ratchet pawl 8a, a pin shaft 8b on which the middle portion of the ratchet pawl 8a pivots, a knob shaft 8c fitted in a hole made in the end face on the large diameter portion 3c of the spindle 3, a spring 8d housed in a side hole of the knob shaft 8c, and a pin 8e that is biased by the spring 8d so as to be pressed into a recess on the back of the ratchet pawl 8a. 
This mechanism is designed so that the location where the push pin 8e presses can be varied by twisting the knob shaft 8c to either the right or the left. When the knob shaft 8c is twisted to the right, the right-hand portion of the ratchet pawl 8a is alternately engaged with and disengaged from the internal teeth 1a of the yoke 1, so that the spindle 3 is rotated in steps to the right. When the knob shaft 8c is twisted to the left, the left-hand portion of the ratchet pawl 8a is alternately engaged with and disengaged from the internal teeth 1a of the yoke 1, so that the spindle 3 is rotated in steps to the left.
Two sides of the yoke 1 is supported by the opposing faces of the retaining elements 2bxe2x80x2 and 2bxe2x80x3 of the distal end bifurcated portion of the housing 2, a guide 9 is fitted in a circular hole formed in the retaining element 2bxe2x80x3 of the distal end bifurcated portion, and a hole snap ring 10 is attached so that the small diameter portion 3b of the spindle 3 is supported by the guide 9. Springs 11 and balls 12 are housed in two or three holes provided so as to be equidistantly spaced in a circle at the step end face of the small diameter portion 3b and large diameter portion 3c of the spindle 3, and the balls 12 are pushed into the guide 9, thus creating a braking force that brakes the free rotation of the spindle 3. Also, the large diameter portion 3c of the spindle 3 is supported while being pressed by a guide 13 that serves as a spring seat, thereby causing the spindle 3 to function as a support shaft for the yoke 1.
The motion converter 7 for converting rotary motion into reciprocal swing motion comprises an eccentric shaft 7a integrally provided at the distal end of the power transmission shaft 6, a ball 7b into which the eccentric shaft 7a is fitted, and a recess 7c formed in a jutting portion of the proximal side of the yoke 1 and in which the ball 7b is engaged.
The above-described power ratchet wrench, however, has drawbacks.
(1) When a bolt is being fastened tightly, or when a tightly fastened bolt is being loosened, the yoke 1 hits the retaining elements 2bxe2x80x2 and 2bxe2x80x3 of the distal end bifurcated portion of the housing 2 while rotating. The inventors discovered the following as a result of investigating this mechanism.
The inside periphery of the internal teeth 1a of the yoke 1 is supported by the large diameter portion 3c of the spindle 3, and thus, the internal teeth 1a of the yoke 1 are inherently worn out quickly. Furthermore, right from the outset there is a large clearance between the large diameter portion 3c of the spindle 3 and the diameter of the internal teeth 1a of the yoke 1, and this clearance grows even larger if the internal teeth 1a of the yoke 1 wears out quickly.
There is also a clearance between the yoke 1 and the retaining elements 2bxe2x80x2 and 2bxe2x80x3 of the distal end bifurcated portion of the housing 2.
Therefore, when the ball 7b engages the recess 7c of the yoke 1 and undergoes planetary rotation that causes the yoke 1 to pivot, the rotational center of the yoke 1 will be greatly shifted with respect to the spindle 3, and the rotational center will also be tilted as the yoke 1 rotate. It is even possible that the yoke 1 tilts around a line perpendicular to both the rotational center of the spindle 3 and the centerline of the ratchet.
The run-out of the yoke 1 when a bolt was being tightened was examined by photography with a high-speed video camera. The examination shows that every time the ball 7b undergoes one planetary rotation, the yoke 1 tilts around a line perpendicular to both the rotational center of the spindle 3 and the center line of the ratchet, then returns, tilts again, returns, and this is repeated.
The yoke 1 hits the retaining elements 2bxe2x80x2 and 2bxe2x80x3 of the distal end bifurcated portion of the housing 2 while rotating. The reason found for this is that the cycle in which the yoke 1 tilts around a line perpendicular to both the rotational center of the spindle 3 and the center line of the ratchet, returns, tilts, and then returns is repeated over and over at high speed, and the yoke 1 repeatedly exerts a wedge action that spreads open the gap between the retaining elements 2bxe2x80x2 and 2bxe2x80x3 of the distal end bifurcated portion.
(2) The function whereby the yoke 1 rotates the spindle 3 in steps becomes unreliable, and it shortens the useful life of the product. The inventors discovered the following as a result of investigation of this shortened product service life.
Very slight vibrations occur between the yoke 1, the spindle 3 and the ratchet mechanism 8, causing repeated impacts of the internal teeth 1a of the yoke 1 against the large diameter portion 3c of the spindle 3. Over time, and within a relatively short time of use, the smooth peripheral surface of the large diameter portion 3c of the spindle 3 becomes uneven, and wear and deformation of the tips of the internal teeth 1a of the yoke 1 are also accelerated. As the unevenness become more pronounced and the wear and deformation proceed, the ratchet pawl 8a no longer meshes at the proper location on the internal teeth 1a of the yoke 1, the meshing operation for stepping becomes unreliable, and it becomes impossible to turn bolts and the like properly.
As discussed above, in the conventional ratchet, the inside diameter of the internal teeth 1a of the yoke 1 is supported by the large diameter portion 3c of the spindle 3, and the yoke 1 is subjected to twisting that results from the repeated tilting back and forth while it rotate. Consequently, the yoke 1 hits the retaining elements 2bxe2x80x2 and 2bxe2x80x3 of the distal end bifurcated portion of the housing 2 during rotation, thus repeatedly exerting a wedge action that spreads open the gap between the retaining elements 2bxe2x80x2 and 2bxe2x80x3 of the distal end bifurcated portion. As a result, the retaining elements 2bxe2x80x2 and 2bxe2x80x3 of the distal end bifurcated portion spread apart, and their clearance from the yoke 1 increases faster than it would otherwise.
In other words, the ratchet pawl 8a becomes no longer to mesh at a proper location on the internal teeth 1a of the yoke 1, the meshing operating for stepping motion becomes unreliable, and thus the bolt and the like cannot be turned properly. These are caused in large part by the fact that the retaining elements 2bxe2x80x2 and 2bxe2x80x3 of the distal end bifurcated portion are spread apart and the clearance between them and the yoke 1 increases faster that it would otherwise.
The inventors examined the spring 8d of the ratchet mechanism 8 by way of using many springs with three different characteristics: wire diameter, winding pitch, and spring length. The springs were installed in the ratchet mechanism 8, beginning with the weakest one and then those having a higher strength. It was found that if the spring is too weak, the meshing of the ratchet pawl 8a with the internal teeth 1a of the yoke 1 becomes misaligned, so that the stepping motion becomes unreliable, sometimes occurring and sometimes not. In contrast, if the spring is too strong, the ratchet pawl 8a remain meshed at the same location without any changes in the meshing position with the internal teeth 1a of the yoke 1, and it does not occur that the ratchet pawl 8a follows the reciprocal rotating motion of the yoke 1, and the spindle 3 follows the rotation of the ratchet pawl; as a result, the spindle does not make a stepwise rotation.
The inventors also examined the braking force that restricts the free rotation of the spindle 3.
The springs 11 were examined by way of using many springs with three different characteristics: wire diameter, winding pitch, and spring length. These springs were installed in the spindle, beginning with the weakest ones and then those having a higher strength. As a result, it was found that if the spring 11 is too weak, there is too little braking force exerted on the free rotation of the spindle 3. If the spring 11 is too strong, the same phenomenon as the strong spring 8d occurs. In other words, the ratchet pawl 8a remains meshed at the same location without any changes in the meshing position with the internal teeth 1a of the yoke 1. Thus, it does not occur that the ratchet pawl 8a follows the reciprocal rotating motion of the yoke 1, and the spindle 3 follows the rotation of the ratchet pawl; as a result, the spindle does not make a stepwise rotation.
It was found that when the strong springs 11 are used and the braking force exerted on the free rotation of the spindle 3 is increased such that the spindle 3 can be halted when the yoke 1 rotates in the direction opposite from the direction in which the spindle 3 is rotated turn stepwise, then the ratchet pawl 8a can properly escape from the yoke 1 of the yoke 1; and during the next rotation of the yoke 1 in the direction in which the spindle 3 is rotated in steps, the ratchet pawl 8a meshes with the internal teeth 1a of the yoke 1 and renders the spindle 3 to make a stepwise rotation.
However, if the distal end bifurcated portion is spread apart, and the clearance of its retaining elements 2bxe2x80x2 and 2bxe2x80x3 from the yoke 1 increases sooner than it would be otherwise, then the same result occurs as when the springs 11 are weak and a lower the braking force exerts on the free rotation of the spindle 3. This was found to be what shortens the service life of conventional ratchets.
(3) The housing 2 must be made from thick steel or iron that is annealed in order to make the housing 2 strong enough so that the distal end bifurcated portion (or the retaining elements 2bxe2x80x2 and 2bxe2x80x3) will not spread apart, and this makes the distal ends of the housing 2 heavier. However, such a housing places a greater load on the user""s arm when the wrench is used for extended periods, making the tool less convenient to use. Furthermore, even if the housing 2 is made from thick steel or iron that is annealed, the distal end bifurcated portion tends to open up (or the distance between its retaining elements 2bxe2x80x2 and 2bxe2x80x3 increases) within a relatively short period of time, making the function of the ratchet pawl 8a that rotates the spindle 3 in steps unreliable.
(4) The motion converter 7, that includes the eccentric shaft 7a, the ball 7b and the recess 7c, is provided next to the yoke 1; and the shape of the housing 2 bulges significantly. As a result, the distal end bifurcated portion (particularly its retaining elements 2bxe2x80x2 and 2bxe2x80x3) cannot be seen during the turning of a bolt and the like in a deeply recessed location, making it more difficult for users to see if the workpiece engagement portion 3a of the spindle 3 is engaged with the bolt, nut, screw or other workpiece.
Accordingly, the first object of the present invention is to provide a power ratchet wrench wherein a structure in which the internal teeth of the yoke are supported by the large diameter portion of a spindle is eliminated, thus making it less likely that whirling occurs in the yoke, and the internal teeth of the yoke is prevented from hitting the peripheral surface of the large diameter portion of the spindle. The early wear and deformation of the tips of the internal teeth of the yoke is thus avoided, assuring that the ratchet pawl meshes with the internal teeth of the yoke and perform its stepping operation for a longer period, allowing bolts and so forth to be turned properly for a longer period. Also, in the present invention, twisting of the yoke due to the friction with motion converter during the rotation of the yoke is less likely to occur, and the force that would spread open the distal end bifurcated portion of the housing is greatly reduced. Thus, the distal end bifurcated portion of the housing is formed strong enough even if made from an aluminum alloy or the like and can be made thinner, thus greatly reducing the weight at the distal end. Accordingly, the load on the user""s arm when the wrench is being used for an extended period is reduced, making the wrench more convenient to use. Moreover, in the present invention, the proximal end next to the distal end bifurcated portion of the housing is formed smaller in diameter than the distal end bifurcated portion. Thus, it is easier in the present invention to see that the workpiece engagement portion which is at the distal end of the spindle is engaged with a bolt and other workpiece, thus making the wrench even more convenient to use.
The second object of the present invention is to provide a power ratchet wrench wherein a structure in which the internal teeth of the yoke are supported by the large diameter portion of a spindle is eliminated, thus making it less likely that whirling occurs in the yoke, and the internal teeth of the yoke is prevented from hitting the peripheral surface of the large diameter portion of the spindle. The early wear and deformation of the tips of the internal teeth of the yoke is thus avoided, assuring that the ratchet pawl meshes with the internal teeth of the yoke and perform its stepping operation for a longer period, allowing bolts and so forth to be turned properly for a longer period. Also, in the present invention, twisting of the yoke due to the friction with motion converter during the rotation of the yoke is less likely to occur, and the force that attempts to spread open the distal end bifurcated portion of the housing is greatly reduced. Thus, the distal end bifurcated portion of the housing is formed strong enough even if made from an aluminum alloy or the like and can be made thinner, thus greatly reducing the weight at the distal end. Accordingly, the load on the user""s arm when the wrench is being used for an extended period is reduced, making the wrench more convenient to use.
The first object is accomplished by a unique structure for a power ratchet wrench of the present invention that comprises:
a housing having a distal end bifurcated portion,
a yoke provided in the bifurcated portion, and
a spindle inserted inside the yoke and having a workpiece engagement portion, a small diameter portion, and a large diameter portion,
wherein a rotary motion of a motor provided on a proximal side of the housing is transmitted through a motion converter that converts a rotary motion into a reciprocal swing motion, thereby reciprocally rotating the yoke by way of using a center line of the spindle as a center of a rotational-motion thereof, so that a ratchet pawl of a ratchet mechanism installed in a space inside the large diameter portion of the spindle is alternately engaged and disengaged from an internal teeth formed around an inner peripheral surface of a hole of the yoke, thus causing the spindle to rotate in steps and causing a workpiece, such as a bolt, nut, screw, and the like, to turn with a workpiece engagement portion provided at one end of the spindle, and
in the power ratchet wrench of the present invention:
the yoke is structured such that the internal teeth are recessed from an end face thereof, guide bushings fitted and fixed in the distal end bifurcated portion of the housing are inserted in the hole of the yoke and support the yoke at both ends thereof, the spindle is inserted and a protruding member is provided to keep the spindle from being pulled out, and the spindle is supported at both ends of the spindle by the guide bushings,
the housing has a small-diameter middle section that is from the distal end bifurcated portion to about half-way toward the proximal side of the and has an external shape narrower than the distal end bifurcated portion so that the distal end bifurcated portion can be seen from the proximal side, and
the motion converter is comprised of:
a swing lever which is provided in an internal space of the small-diameter middle section of the housing,
a boss which is provided at an approximate middle point of the swing lever and is rotatably disposed on a pivot shaft which is provided in the small-diameter middle section of the housing so as to be parallel to the spindle,
an engagement portion which is provided at one end of the swing lever and has a groove-shaped recess formed at a proximal end of the swing lever, the groove-shaped recess fitting on a ball provided on an eccentric shaft of a speed-reduction assembly provided in the housing, and
a cylindrical portion which is formed at another end of the swing lever and is slidably engaged with a U-shaped groove formed in a jutting portion of a proximal side of the yoke.
The second object is accomplished by another unique structure for a power ratchet wrench of the present invention that comprises:
a housing having a distal end bifurcated portion,
a yoke provided in the bifurcated portion, and
a spindle inserted inside the yoke and having a workpiece engagement portion, a small diameter portion, and a large diameter portion,
wherein a rotary motion of a motor provided on a proximal side of the housing is transmitted through a motion converter that converts a rotary motion into a reciprocal swing motion, thereby reciprocally rotating the yoke by way of using a center line of the spindle as a center of a rotational-motion thereof, so that a ratchet pawl of a ratchet mechanism installed in a space inside the large diameter portion of the spindle alternately is engaged with and disengaged from an internal teeth formed around an inner peripheral surface of a hole of the yoke, thus causing the spindle to rotate in steps and causing a workpiece, such as a bolt, nut, screw, and the like, to turn with a workpiece engagement portion provided at one end of the spindle, and
in the power ratchet wrench of the present invention:
the yoke is structured such that the internal teeth are recessed from an end face thereof, guide bushings fitted and fixed in the distal end bifurcated portion of the housing are inserted in the hole of the yoke and support the yoke at both ends thereof, the spindle is inserted and a protruding member is provided to keep the spindle from being pulled out, and the spindle is supported at both ends of the spindle by the guide bushings.